(1) Technical Field
The present invention relates to a method for treating an exhaust gas and an apparatus therefor which can efficiently carry out a treatment of separating a noxious and malodorous gas and concentrating the gas to a small flux. The method is for treating low concentration exhaust gases containing fine particles and a noxious and malodorous gas component, such as exhaust gases from car coating. In low concentration exhaust gases containing fine particles and a noxious and malodorous gas, the fine particles, for example plasticizers, higher fatty acids, lampblack, pitch, etc., may deteriorate an adsorbent. Such exhaust gas is also produced in printing, steel pipe production presses, etc.
The meaning of "fine particles" as mentioned in the specification includes, generally, adhesive dust, mist and particulate high boiling point substances. "Mist" means liquid fine particles, and the "high boiling point substances" mean a high boiling point gas and a high boiling point mist.
(2) Background Art
A so-called deodorizer for separating a noxious and malodorous gas from an exhaust gas containing a low concentration noxious and malodorous gas such as organic solvents, etc., is widely used in manufacturing processes in various industries. A typical prior art example of a deodorizing treatment of this type appears in FIG. 1 as an apparatus for treating an exhaust gas from a car coating process.
A coating booth 201 in a line for coating car chassis generates an exhaust gas containing adhesive dust consisting of very fine paint residue with a not more than 10 .mu.m particle diameter and a noxious and malodorous gas component such as organic solvents. This exhaust gas needs to be purified. Therefore, the exhaust gas is dusted by initially passing the exhaust gas through a wet static dust collector 202 via an exhaust pipeline 14. At this time, for preventing dust from sticking to the electrodes, a sprinkling on the dust collector electrodes is performed. The dusted exhaust gas is fed to a humidity/temperature regulator 203 to be dehumidified and adjusted in temperature. Thereafter, the noxious and malodorous gas component of the exhaust gas is concentrated and separated in a honeycomb type concentration apparatus 204. The purified and treated air is again fed to the coating booth 201, passing through another humidity/temperature regulator 205 via a pipeline 19. The noxious and malodorous gas concentrated by the concentration apparatus 204, after being separated, is discharged out of the room through a heat recovering and exchanging device 207 as an exhaust gas after being neutralized by oxidation treatment in a catalytic oxidation apparatus 206.
As apparatuses for direct treatment of an exhaust gas, there are available directly firing furnaces, catalytic oxidization apparatuses, adsorptive recovery systems, chemical solution cleaning systems, etc. These apparatuses become further economically disadvantageous with decreasing concentrations of contaminants. As treatment systems combining small devices, with the exhaust gas once concentrated to provide a small flux, of primary interest now is the above-described concentration apparatus 204 making use of a rotor formed in a honeycomb shape of an adsorbent such as activated charcoal, etc. This apparatus is advantageous in its excellent operational economy, but involves the below-mentioned problems.
Because the adsorbent is formed into a honeycomb shaped rotor, the cost of the apparatus is over ten times as high as the material adsorbent. Moreover, because the adsorbent is formed in an admixture with an organic binder and auxiliary materials, its reactivation is difficult when its adsorptive performance has deteriorated. Furthermore, because of its heating system using hot blast for regeneration in order to concentrate the exhaust gas, indirect heating is not applicable. As a consequence, the degree of concentration is limited to 10 to 15 times on account of the heating calories for the honeycomb rotor, and simultaneous heating of not only the adsorbent, but other combined members, like the auxiliary materials, etc., is necessary, thus requiring large heating calories therefor.
Particularly, in the case of the treatment of the exhaust gas from car coating, because of the adhesive dust being contained in the exhaust gas, this adhesive dust sticks on the surface of the honeycomb shaped rotor, thereby blocking the rotor, and resulting in an extremely lowered adsorptive performance. This necessitates its combination with a wet static dust collector 202 with a high performance and high price, raising the problem of a high overall cost of the equipment.
On the other hand, the exhaust gas produced in printing processes contains high boiling point substances, such as plasticizers and wood tar, which could deteriorate the adsorbent forming the honeycomb shaped rotor. This necessitates the use of an expensive floor-fixed type adsorption tower as pretreatment equipment, which also increases the overall cost of the equipment.